This invention relates generally to the field of turbochargers and, more particularly, to an improved cambered design for vanes disposed within a variable geometry turbocharger for purposes of maximizing flow efficiency within the turbocharger.
Turbochargers for gasoline and diesel internal combustion engines are devices known in the art that are used for pressurizing or boosting the intake air stream, routed to a combustion chamber of the engine, by using the heat and volumetric flow of exhaust gas exiting the engine. Specifically, the exhaust gas exiting the engine is routed into a turbine housing of a turbocharger in a manner that causes an exhaust gas-driven turbine to spin within the housing. The exhaust gas-driven turbine is mounted onto one end of a shaft that is common to a radial air compressor mounted onto an opposite end of the shaft and housed in a compressor housing. Thus, rotary action of the turbine also causes the air compressor to spin within a compressor housing of the turbocharger that is separate from the turbine housing. The spinning action of the air compressor causes intake air to enter the compressor housing and be pressurized or boosted a desired amount before it is mixed with fuel and combusted within the engine combustion chamber.
In a turbocharger it is often desirable to control the flow of exhaust gas to the turbine to improve the efficiency or operational range of the turbocharger. Variable geometry turbochargers (VGTs) have been configured to address this need. A type of such VGT is one having a variable or adjustable exhaust nozzle, referred to as a variable nozzle turbocharger. Different configurations of variable nozzles have been employed in variable nozzle turbochargers to control the exhaust gas flow. One approach taken to achieve exhaust gas flow control in such VGTs involves the use of multiple vanes, which can be fixed, pivoting and/or sliding, positioned annularly around the turbine inlet. The vanes are commonly controlled to alter the throat area of the passages between the vanes, thereby functioning to control the exhaust gas flow into the turbine.
The vanes are generally designed having an airfoil shape that is configured to both provide a complementary fit with adjacent vanes when placed in a closed position, and to provide for the passage of exhaust gas within the turbine housing to the turbine wheel when placed in an open position. It has been discovered that the airfoil shape of conventional vanes used in such application creates an undesired back-pressure within the turbine housing that does not contribute to the most efficient turbocharger operation.
It is, therefore, desired that the vanes for use with a variable geometry turbocharger be configured in a manner that minimizes any unwanted aerodynamic pressure effects within the turbine housing to facilitate and promote efficient turbocharger operation. It is also desired that such vanes be designed in a manner that facilities use of the same within variable geometry turbochargers with minimum adjustments or retrofit changes.
Improved cambered vanes of this invention are constructed for use within vaned turbochargers, including but not limited to a VGT. The VGT comprises a turbine housing having an exhaust gas inlet and an outlet, a volute connected to the inlet, and a nozzle wall adjacent the volute. A turbine wheel is carried within the turbine housing and is attached to a shaft. A plurality of such improved cambered vanes are movably disposed within the turbine housing between the exhaust gas inlet and turbine wheel.
Each improved cambered vane comprises an inner airfoil surface oriented adjacent the turbine wheel, and an outer airfoil surface oriented opposite the inner airfoil surface. The inner and outer surfaces define a vane airfoil thickness. A cambered vane leading edge or nose is positioned along a first inner and outer airfoil surface junction, and a vane trailing edge is positioned along a second inner and outer surface junction.
The vane inner and outer airfoil surfaces, in conjunction with the vane leading edge, are specially configured to provide a vane camberline, as measured between the airfoil surfaces and extending along a length of the vane, that has a gradually curved section and a substantially flat section. Vanes of this invention have characteristic camberlines that are flat for at least the first 5 percent of the vane length moving away from the vane leading edge. Vanes configured in this manner have a leading edge and transitional outer and inner airfoil surfaces that reduce unwanted aerodynamic effects within the turbine housing by maintaining a constant rate of exhaust gas acceleration as exhaust gas is passed thereover, thereby reducing unwanted back-pressure within the turbine housing and increasing turbocharger and turbocharged engine operation.